Selecting and lockout circuit



p 1952 Q G. HECHT 2,609,454

I SELECTING AND LOCKOUT CIRCUIT Filed June 29, 1948 Wvsmvk G. HE CH T ATTORNEY Patented Sept. 2, 1952 UNITED STATES PATENT OFFICE SELECTING'AND LOCKOUT CIRCUIT George Hecht, Astoria, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York ApplicationJuneZB, 1948, Serial No. 35,851

This invention relates specifically to improvements in selecting systems and more specifically to improvements wherein a non-linear impedance is used to decrease the probability of more than one circuit being selected.

' One of the primary objects ofthis invention is to decrease the probability of more than one circuit being selected for use.

A second object of the invention is to utilize a non-linear impedance element as a common impedance to a plurality of space discharge tubes so as to prevent more than one discharge tube from ionizing during the same selecting operation by limiting the potentials of the other discharge tubes to a value less than that necessary for ionization.

A further object of the invention is to improve the operation of selecting systems generally.

The invention consists of 'a plurality of selectcausing a decrease in voltage applied to the control gaps of the discharge tubes. This decrease in applied voltage acts to lock out, or prevent from ionizing, all the space discharge tubes except the one which :was drawing the most current. This lock-out effect is believed to take place within microseconds and before the current has risen above a few microamperes. This last-mentioned tube then ionizes completely and the current flow therethroughis'large, which causes theresistance of the common non-linear impedance to'decrease so that a current suflicient to operate relays can flow through the ionized tube. The advantage of using a non-linear impedancethat there 'is' much less' chance of more than one'space discharge tube ionizing since there is a large enough voltage drop across the non-linear impedance, at the time of ionizationof the control gap of said one tube, to successfully prevent any other tube from ioni'z -In the prior art there are several devices whereby a common resistance or common inductance has been used in series with a number of gas tubes connected in parallel with respect to each other. The function of these devices has been to Dre:

' elude more than one tube from ionizing.

Claims. (01. 179 18) would ionize.

In the instance of the common resistance however, there was a chance that more than one tube To correct this deficiency a common inductance with resistance was used. It was found that the probability of more than one tube ionizing was considerably less than in the case where a resistance alone was used. But the use of the inductance presented a new problem, e. g., that the current was prevented, due to inductance in the common impedance from risingrapidly to a sufficient value to operate relays after the tube had ionized.

The objects of this invention are accomplished by constructing the non-linear impedance so that the potential drop across the impedance'is greatest at the time before any of the control gaps of the tubes ionize, and so that potential drop across the impedance remains large enough while one of the tubes is ionizing to successfully prevent any 'othertube from ionizing, and finally so that after one of the tubes has ionized the impedance of the non-linear resistance, although considerably decreased, remains large enough to prevent any other tube from ionizing. This feature of the invention thus eliminatesmuch 'of the possibility of more than one tube ionizing. Since there is no appreciable inductance present in the non-linear impedance there is less time lag between the ionizing of the main gap of the space discharge tube and the operation of the relay than if an inductance had been used. It can be seen, therefore, that this invention combines the advantageous features of both the inductive andresistive common impedances, and at the same time, eliminates those features which are disadvantageous; The incorporatedadvantageous features are the decreased probability of more than one gas tube ionizing and the decreased time lag between the ionizing of a gas tube and the increase of current therethrough to a value suflicient to operate a relay. In the telephone art time savings of milliseconds in operations which are repeated many times an hour: are of economic importance.

The aforementioned features and other features of the invention willbe described more fully in the following detailed description.

This invention is applicable generally to selecting and connecting systems but is'disclosed in the drawing as used with a' cross-bar switch in a telephone system. For explanation of crossbar switch "structure and operation, reference is made to Patent 2,021,329, issued to Reynolds, November 19,1935.

.Referring to the drawing, the subscribers lines I (ll, I02, etc, appear in the vertical rows and the outgoing lines appear in the horizontal rows 3 I23, I64, I05, etc. Individual line relays I06, IIlTl etc. and switch hold magnets I38, I29, etc. co operate with the subscribers lines, and select magnets III}, III, II2, etc. cooperate with the together through condensers I32, I33, I35, etc. to positive battery I39 through armature of relay I26. The cathodes I22, I23, I24, etc. of the tubesare all electrically connected to negative battery I28 through armature of relay I26. The starting electrodes IIE, I I8, II9, etc. of the tubes are electrically connected through test conductors II'I,

I26, I2I, etc,respectively'through armatures of relays I35, I31, 1612; etc. respectively, to positive batteries I36, 138,. i3ii, etc., respectively. Each of the anodes I29, I38, I3I', etc. is connected to one of the selectrinagnets H9, II I, II 2, etc.,.re'- spectively. The non-linear impedance I21, which is a common impedance to all the tubes,.is connected tolnegative battery I28.

The operation of the invention will now be described in detail. A subscriber of line IOI picks up his receiver- This closes the circuit through lines IiiI and the winding of relay I95, thereby energizing relay I86. A circuit is thus completed from ground through the armature of relay I06, the winding of relay I26, to negative battery, and thence to ground, energizing relay I26, and closing-the contacts of. relay I26. This places positive 100 volts on the anodes of the tubes through the left armature'of "relay, I2% and the select magnets, III), III, Iii-2, etc. It also places negative 50 voltson the leit cathodes of the tubes through the -right-'hand armature of relay I26. Thus there is a difierence of .potential'of 150 volts between,v the anodes and the left cathodes of the tubes,but this is insuficient to ionize the tubes. There is, however, a positive voltage of batteries I36, I33,- IIl3, etc. applied tothe right-hand starting electrodes of the tubes through conductors I11, I28, I2I, etc. respectively. This creates'a differences ofpoten-tial between thecathodes and But only one ionized the potential drop across the non-linear impedance I21 is less than it was before ionization, but it is still large enough to preclude any other of the discharge tubes from ionizing. It can be seen, therefore, that the use of this nonlinear impedance I2'I decreases the probability of more than one tube ionizing. ,v

Before relay llii canoperate, however, the ionization within the tube H3 must transfer to anode I29, so that an arc will exist between cathode I 22 and anode I29. Conduction is eficcted between cathode I22 and anode I29 after ionization has been established between cathode I22' and startingelectrode II6. After the transently differentcharacteristics and one of them,

tube II3.-fcr example,-will begin to pass a little more space-current than the others. "As this ini tial spacecurrentis-srnall compared to operating value, alarge potential drop is created in nonlinear impedance I 27., This potential drop reduces the applied voltage across the tubes and prevents'thc tubes, otherthan-tube II3,:- from ionizing; As longgasthe current throughtube H3 is small therewill be a large potential drop across the non-linear impedance I2] which will keep the othertubes from ionizing.

The non-linear impedance lil'Iis -so designed that the potential drep'across it is largest when the current passing through itis smallest.-. Thus, up until the time of ionization of tube II3 the potential drop across the non-linear impedance is at its largest value and will prevent any other tube from ionizing. =When the tube IIS is fully fer is made a completed circuit exists through positive battery I39, line I IB, winding of select magnet I Iii, anode I29, across the space gap to cathode I22, line I25, through non-linear impedance I27, to negative battery I28. Select magnet III) is operated almost immediately as non.

linearimpedance I21 contains no inductance.

'Thevoperationof select magnet IID prepares the horizontalrowof cross-barcontact's, which appear in outgoing circuit. I03, for further operation. Thereafter in any suitable imanner a circuit isclosed over conductor MI for the operation of holdmagnet I03. The operation of hold magnet I68 closes the said cross-bar contacts and establishes a. circuit from the subscribers telephone to the outgoing circuit I03. At this time-relay I35 which is under the control of the supervisory relay (not shown), operates to place ground potential upon the starting electrodeand provi'desa holding circuit to ground for hold magnet I08. Since the voltage of battery I28 is insufficient to sustain an arc across the gap.I.22- II6, said are is extinguished. Relay I35 willfremain energizedas long as the subscriber of line IIII continues his call.

Referring again toh'old magnet I08 which has just been energized over lead I iI, it can be seen from the drawing'that such energizationof hold magnet I08- opens lines IBI to deenergize relay HIE-which in turn causes relay I28 to deenergize. Dceneigization of relay I26 opens the circuit from positive battery'l3 9, armature of relayxl26, line'ldil, select magnet I I9, anode I29, spacetgap to'cathode I22, line I25, armature oi reIayLI-ZB, non-linear impedance I2'l, to negative battery I28, deenergizing select magnet III) and extinguishing tube H3, If the subscriber in line I02 should-attempt to place a call, tube I I3 would not be afiected since relay I35 is energized and. the armatureof relay I35 connects starting ielectrcde 'I It to ground through line II'I causing potential diiference between'cathode I22 and starting'electrode H6 to be insufiicient to ionize tube 3oz, 1

nthe subscriberof line IIiIhangs up his receiver the supervisory relay (not shown) operatestc deenergizerelay I35; Deenergization of relay-1.35 opens the holding circuit for relay I I38- which thenbecomes deenergized. -In addij-. tion, the deenergization of relay I35 .places1 a positive battery I36 on start electrode IIE gto make-tube- II3' again ready foranother subscriber:

In; addition to the non-linear impedance I21 acting-to keep the'tubes, other than tube H3; from ionizing, condensers I32, I 33, I34, etc. also act to-iurther-decrease the voltage applied across anodes 'zand cathodes 'of tubes I other than tube 1 113D "This is accomplished as "follows: When tube II3st'art's tdionize,'current'passe's through It, causinga difference 7 of potential across said holding magnet. A current will fiow from the positive side of said select magnet, alongline I40, through select magnet II I, and will charge condenser I33. This charging current will'produce a voltage drop across select magnet lll'and further-decrease-the voltage applied to anode I30. Similar circuits ,and charging currents will lower the anode voltage oftubell5.

What is claimed is:

-1. In an arrangement for interconnecting any one circuit of a first group of circuits to any circuit of a second group, the combination comprising a plurality of gaseous -discharge tubes, each including a main space path and a control space path, a power source, a resistance element having a negative current coefficient of resistance, individual control means for said first circuit operatively responsive to a calling condition, connecting means rendered effective responsive to operation of the individual control means of any of saidrfirst group of circuits for connecting said resistance element and said power source to the control space paths of said gas discharge tubes, whereby said control space paths are connected in a low impedance parallel connection with respect to one another and the combination thereof is connected in series with said power source and said resistance element through said connecting means when any one of said first group of circuits requests to be connected to one of said second group of circuits thereby applying an ionizing potential to said control space paths through said resistance element, a second power source, a plurality of actuating means individually connected to each of said main space paths, means connecting said second power source to all of said actuating means, one of said actuating means interconnecting one of said second group of circuits associated therewith to the calling one of said first group of circuits, said resistance element preventing more than one of said control space paths from being ionized at the same time by developing a potential thereacross opposing the potential of said first power source incident to the ionization of one of said control space paths, the resistance of said element thereafter being reduced due to current flow therethrough so as to facilitate rapid operation of the actuating means associated with said ionized main space said devices is to be fully ionized within a short r time interval to the exclusion of the other of said devices, each of said devices comprising a main space path and a control space path, a power supply, means connecting said power supply with the main space path of each of said devices, a plurality of impedance elements individually connected in series with a different main space path and said power supply through said connecting means, said control space paths connected in a low impedance parallel connection, a resistance element having a negative current coefiicient of resistance connected through said connecting means in series with said parallel connected control space paths, said resistance element preventing more than one of said control space paths from being ionized at the same time by developing a potential thereacross opposing the potential applied to said parallel thereby locking-out the other of saidparallel connected control space paths and said resist ance element thereafter reducing its resistance value due'to increased current flow therethrough so as to prevent a, high value surge potential from being developed thereacross' due to ionization transfer toone'of said main space paths thereby diminishing the time interval during whi ch the impedance element associated with said ionized main space path attains peak potential thereacros s. I I

3; In an arrangement employing a plurality of gas discharge devices each including a main space path and a control'space path, a load impedance element connected in each of said main space paths, means connecting said control space paths in a low impedance parallel circuit, a powersupply'for saidcontrol paths and-said main paths, respectively, a resistance element having a negative current coefficient' of resistance connected in series with" said control paths power supply, *and means for connecting said power supplies to said space paths substantially simultaneously, said negative resistance element developing a potential thereacross opposing the potential applied to said parallel connected control space paths incident to the ionization of one of said control space paths to effectively reduce the potential applied to said gas discharge devices to prevent ionization of the control space paths of, another of said devices.

4. In an arrangement for interconnecting any one of a first group of lines with any one of a second group of lines, the combination of a plurality of gas discharge tubes each having an anode, a cathode and a control electrode, each tube individual to a different second line, oppositely poled first and second power sources, individual control means for each first line operatively responsive to a calling condition thereon, means common to said first and second lines operated responsive to operation of the individual control means of any first line for connecting one of said power sources to the anodes! of said tubes and the other of said power sources to the cathodes of said tubes, a resistor element normally having a high resistance and having a negative current coefficient of resistance connected in series with said other power source and each of said cathodes, current discharge being initiated between the control electrode and cathode of some one of said tubes responsive to operation of said common means followed by current dischargebetween the anode and cathode of said tube, the normally high resistance of said resistor element blocking initiation of discharge in any other of said tubes, and individual means for each of said second lines operatively energized by the current discharge between the anode and cathode of the associated tube to establish connection of a calling first line to the second line with which said energized tube is individually associated, the decrease in normal resistance of said resistor element upon initiation of current discharge in any tube effecting fast operation of the individual means of the second line with which said energized tube is individually associated.

5. In combination a first plurality of lines, a second plurality of lines, a switching device comprising contact means for interconnecting any one of said first lines and any one of said second lines, electromagnets one for each of said second lines, and hold electromagnets one for each of said first lines, gas discharge tubes one for each of said second lines, a first source of positive electrical. potential with respect to ground; me n individual to each second line normally connecting the start anode of the indiuidualgas discharge tube to said first source of positive potential, a source of negative electrical potential with respect to ground,v a resistor having a normally high impedance and a negative current .coeflicient of resistance, relay means individual to each "first line operated to :request interconnection of the first line to any idle one of said second lines, relay means common to said first lines rendered eiiective by operation of the individual relay means of any first line for-closing a .connectionfrom the cathodes otall of said gas discharge tubes in parallel through said resistor to said source of negative potential, a second source of positive electrical potential with'respect toground, means including said common relay means for connecting said second source ofpositivexpotential through the winding of each of said select electromagnets to the main anodes of the gas discharge tubes thereby effecting :the energization of the :most sensitive one of said gas discharge tubes individually associated, with an idle one of said secondlines and the energization of the individually associated one of said select electromagnets, and contact means closed by operation of the energized one of said select electromagnets to connect the winding of the hold electromagnet of a first line the individual relay means of which is operated to the start electrode of the gas discharge tube individually associated with the energized one of said select electromagnets. 7

GEORGE HECHT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS asaaese' Cl"1ristian Jan. 2?, 194a 

